Spasticity is a common complication in MS (Multiple Sclerosis) and occurs in up to 84% of patients. The main sign of spasticity is resistance to passive limb movement characterized by increased resistance to stretching, clonus, and exaggerated deep reflexes. The associated features of spasticity, including pain, gait disorders, fatigue, and loss of function, significantly affect patient quality of life. Data collected from the North American Research Committee on MS (NARCOMS) Patient Registry showed that 34% of over 20,000 MS patients surveyed experienced moderate, severe, or total limitation of abilities due to spasticity.
Baclofen (racemic baclofen: rac-BAC; (+/−)-4-amino-3-(4-chlorophenyl)butanoic acid) is a GABAB receptor agonist that has been used in the United States since 1977 for alleviating the signs and symptoms of spasticity resulting from multiple sclerosis or spinal cord injury. The mechanism of action of baclofen in spasticity appears to involve agonism at GABAB receptors of the spinal cord (Price et al., Nature 1984, 307(5946), 71-4). Baclofen is believed to inhibit the transmission of both monosynaptic and polysynaptic reflexes at the spinal cord level, possibly by hyperpolarization of primary afferent fiber terminals, with resultant relief of muscle spasticity. Baclofen was approved for marketing as a racemic compound; however, preclinical studies have since demonstrated that the antispasticity activity of the drug resides exclusively in the R-isomer (Albright et al., Neurology, 1995, 45(11), 2110-2111).
The active isomer (R)-baclofen ((L)-baclofen; (−)-baclofen; ARBAC) has also been studied in several clinical trials for the treatment of trigeminal neuralgia, affective disorder, and cerebral spasticity. It has been demonstrated as providing or suggested to provide efficacy in spasticity, spastic diplegia, spasticity associated with multiple sclerosis, amyotrophic lateral sclerosis, trigeminal and glossopharyngeal neuralgias, spinal cord injury, alcoholism, alcohol addiction, dependence or alcohol abuse, gastro-esophageal reflux disease (GERD), emesis, cough, narcotic addiction or abuse, nicotine addiction or abuse, neuropathic pain and musculoskeletal pain, nocturnal acid breakthrough, chronic hiccups, dyspepsia, non-nuclear dyspepsia, gastric motility disorder, migraine, PTSD (Post-traumatic Stress Disorder), depression, anxiety, and lower urinary tract dysfunction.
Baclofen has a number of significant pharmacokinetic limitations including a narrow window of absorption in the upper small intestine and rapid clearance from the blood. Consequently baclofen in immediate release (IR) form is taken three to four times per day to maintain the therapeutic effects. The product literature for LIORESAL® baclofen (an immediate release tablet formulation) indicates doses can be taken in the fed or fasting state with no substantial effect upon pharmacokinetic parameters. There have been no reports in the literature of baclofen (either in racemic or in optically pure or enriched form) exhibiting any positive or negative food effect in any dosage form.
Extended release, sustained release, controlled release and modified release dosage forms containing racemic baclofen (rac-BAC) or (R)-baclofen (ARBAC) are known and reportedly useful for reducing the number of dose administrations per day since they increase the period of drug release and reduce the Cmax as compared to the IR dosage form. Merino et al (Proc. Eur. Congr. Biopharm. Pharmacokinet., 3rd (1987), 2, 564-73) describes studies of intestinal absorption of baclofen in the rat small intestine. Merino concludes that administration of sustained-release forms of the drug or the use of increased doses of baclofen to obtain better therapeutic responses may not be suitable for clinical practice in humans.
It would be a significant addition to the art to provide a controlled release dosage form suitable for once or twice daily oral administration that still provides therapeutic levels of ARBAC for an extended period of time without having to increase the dose of ARBAC as compared to repeated doses of an IR dosage form in a day.